Electromagnetic device



Oct. 13, 1931.

R. E. H. CARPENTER 1,826,990

\ ELECTROMAGNETI C DEVICE Filed April 4, 1929 2 Sheets-Sheet l /NVENTOP ELECTROMAGNETIC DEVICE Filed April 4. 1929 .A2 Sheets-Sheet 2 Patented Oct.y 13, 1.931`

UNITEDy s'rairEsl PATENT ol-FlcE `f RUPERT EVAN HOWARDMCARPENTEB, or PUnLE-Y, ENGLAND ELEcrRoMAGNnrIc DEVICE Application led April 4, 17929, Serial No. 352,494, and lin GreatBritain April 25, 1928.

' if.) sponding to currents or potentials applied to the machine or instrument, such as 1s necessary, for example, on the one hand in electromagnetic motors, or on the other hand in electromagnetic relays, and the driving units employed in sound reproducing instruments. However, the invention is also applicable to machines depending upon the converse action, namely, the production of an electro-y motive force dependent upon the driving of il@ a moving member as,` for example, is the case in magneto-electric machines employed in ignition for internal combustion engines and other electric generators. l 7

There are a number of points which require careful consideration in the design of the magnetic circuit of an efficient relay or similar electromagnetic device. The part of themagnetic circuit acted upon by a reversals coil, which may be called the reversals cir,- cuit,should have minimum reluctance, and the ktotal reluctance of this circuit should only be slightly greater than that of the air gaps and the core carrying" they reversals winding, whilst as much as possible ofthe iux change produced by the current in the reversals coil should operate on the armature, Again the hysteresis and eddy curreni` losses in that reversals circuit should be as small as possible, and shouldfbe limited substantially to the losses in the-.core carrying the reversals winding. i c

In. order to obtain thesetwo conditions, it is necessary to arrange forthe steady polarizing flux not to pass through the core carry 45 ing the reversals Winding, and to make those portions .of magnetic material traversed by both the fluctuating flux and the steady polarizing fiux of large cross-section lfor two reasons: First, allr known ferromagnetic kma- 50 tei-.iai has the property that thepresence of Aa winding.

are only subject to small variations. Thus,

steady flux greatly reduces the incremental permeability of thematerial, and secondly any desired intensity .of polarizing flux may be employed without any limitation which kwould otherwise be imported by the crossn; section' of the core carrying the reversals The next point is that the armature should have a minimum vmoment of incrtia, andas a secondary matter, should be mounted in such a wayv that bearings or pivots, if they are used, shall be readily accessible. Onepair of air gafps should be employed since the use of two pairs, particularly if the axis of. oscillation of the armature lies between them, increases considerably the 6; accuracy needed in manufacture., and in any case for aygiven change of reluctance for unit movement of the armature, air gaps of only one-half the lengthmust be employed when two pairs ot a given cross-sectional area are arranged in'series in the reversals circuit. A.

' bias adjustment should be provided gradual in its action but not dependent upon great mechanical nicety of manufacture. Further, it is advantageous to employ only onek spool for thc reversals winding surrounding a stationaryy core and easily replaceable if it should be burned out. f

It isthe principal object of the present inventionto provide a magnetic circuit which lends itself to a design inwhich all these advantages can be combined in a Way which hasr not been possible previously, and at the ksame time to keep the manufacturing cost very low.

According to the present invention, the magnetic structure of a device liof the above kind consists of a portion having a magnetic circuit of low reluctance to carry the fluctuating fluX, and a portionof relativel large reluctance inwhich the steady flux lbws in two parallel-paths, the reluctanceof the latter portiony is suflicient to avoid serious shunting with respect to the fluctuating flux ofthe part of the' magnetic circuit of low reluctance in which the effective air gap is disposed. iThus, steady lluxesypreferably equal in value, flow in the ktwo 'parts of the high reluctance part of the magnetic structure and when the invention applied to an electromagnetic relay the vibratory armature is located in a gap between the pole faces of two limbs, preferably ot relative-ly large crosssection, and the circuit for the fluctuating ilui; is completed by a bridge-piece which carries the coil ot' the instrument, and may be of smaller cross-section than the said limbs, because this bridge-piece does not have to carry the steady or polarizing flux. The divided part- Vof the magnetic struc-ture in which the latter Hows may consist of a pair ot permanent magnets, the like poles of which are connected. to al central limb of the magnetic structure on which the vibratory armature is supported.

This construction enables the bridge-piece to be formed of laminated material, and to be readily removed and replaced by a piece carrying a coil ot' dill'erent resistance. Moreover, the construction allows of very conv `iient 'forms of biassing. Biassing may be eil'ected by employing a wandering or adjustable magnetor magnetic member which can be set into a position so as to shunt, or in the case of a magnet, either to shunt or assist one or other of the two permanent magnets of the instrument until any steady flux in the bridge-nece carrying the coil is neutralized.

In order to render the invention clear, and to enable same to be carried into eilect without diliiculty, a form lo'l.E telegraph relay and a torni of small rotary motor constructed in accordance with the invention, will be described in greater detail with reference to the accompanying drawings, wherein:

Figure 1 is a rear elevation of a relay with the biassiug magnet shown 'broken away;

Figure 2 is an elevation seen from the left oi Figure 1; while Figure 3 is a ,plan with the coil and the base removed;

Figure 4 is an enlarged cross-section show ing the method of clamping t-he butts of the relay in `their adjusted positions,

Figure 5 is an elementary diagram of the magnetic circuit employed; and

Figure G is a diagrammatic elevation of a small rotary motor constructed in accordance with the invention.

Referring tirst to Figures land 2, the magnetic structure comprises a lower horizontal limb 1 lconnected near its outer end 'by two permanent magnets 2, 3 to limbs 4, 5, which form the part of the low reluctance magnetic circuit through which the steady flux passes. The magnets 2, 3 are made of cobalt lsteel or similar material ot' high retenftivity and coercivity. Like poles of the two magnets are connected to thehorizontal limb 1, and mounted on the central part o't' the limb 1 is the central member 6 ot the system, Vso that flux from the magnets 2 and 3 pass lin parallel through the member 6 inthe same direction. The armature 7 of the relay carrying the tongue 8 is shown pivoted to the central limb 6, it being carried by short blade springs 9 clamped innon-magnetic brackets 10, so that the downward pull on the armature T places the springs 9 in tension. The armature 7 could, however, be carried on a knife edged pivot on the limb G, and in the case of a driving element, for example, for a loudspea-king telephone receiver, the member 6 could be pivoted at its lower end and itself form the Vibratory reed. rl`he butts 11,` 12 of the relay are adjustably carried in pillars 13, 14 which are carried on thc limbs 4, 5 and insulated therefrom, for example, by mica washers.

`The method of clamping the butts is illustrated in greater detail in Figure l, which shows the pillar 13 in vert-ical section. The vertical bore through the centre of the pillar 13 is tapped and a hfrlzontal hole 15 is drilled at right angles to it. The screwed stud 16 screwed into the lower part of' the bore and serves for [fixing the pillar 13 to the limb 4.

The stem 1T ofthe butt 11 is passed through the hole 15 into which it is screwed by a tine thread, and after linal adjustment is clamped by dropping a small hardwood plug 18 on to it in the bore in the pillar 18 and clamping the plug -down finally vby a screw 19, this avoids any difliculty in screw-threading the pillars 13, 14, and avoids the use of split pillars and complicated clamping devices. The limbs 1, 5 are L-shaped in plan, as seen in Figureg, and their outer ends are connected by the laminated bridge-piece 20. The latter is shown let into notches in the members L1 and retained in position by clamping pilates .'21 which can be readily removed to allow the bridge-@piece 2O to be taken away and replaced by another bridge-piece with a coil of didier-ent resistance. The whole of the reversals circuit comprising the limbs 4, 5 and the bridge-.piece 2O can be made laminated, in which case alternate plates of two dierent shmpes are employed so as to provide lap joints yand not butt joints in order vto reduce the total reluctance. The construction then is similar to the construction of small transformer cores, the plates being clamped together, for example, by screws and clampingr plates. The 'coil 22 is carried on the bridge-piece 20, the connecting wires for receiving the incoming signalling currents being shown at 23. At 2l are the connecting wires from the tongue 8 and the butts 11, 12 of :the relay; the connecting wires are taken to :appropriate yterminals such .111525, 26.

It will be lseen that the two magnets 2, `3 with the central limb 6, and the lower limb 1 form two similar vhalves of a structure exterlnal to the magnetic circuit carrying the varying flux. These two similar :and equal halves fare of relatively high reluctance. Air gaps, or saturated portions of reduced area '59 convenient forms of biassing'.` If, iny the may be' inserted inthe divided branches to increase the reluctance 4particularly when electromagnets are employed for polarizin The bridge-'piece 20 carrying the reversa s coil 22 is shown of smaller cross-section than the members 4,5 forming the elongated polepieces. This is a convenience as regards the design of the coil 22, but it does not interfere with yobtaining low reluctance over the .complete magnetic circuit'yfor the varying flux, since among other things the bridge-piece 20 forming the core of thecoil 22 does not carry the polarizing flux, and it isknown that the permeability of a limb of a magnetic structure is in general reducedby the presence of an appreciable steady magnetization. By means ot thisl construction not only is the part of the magnetic structure forming the path for the steady flux external to the circuit ior the varying flux divided into two independent portions in which equal fluxes flow which are maintained substantially constant under all conditions, but those two halves of the external part .of the magnetic structure are themselves of relatively high reluctance and therefore do not form any magnetic circuit substantially shunting with respect to the reversing flux the part of the local circuit which contains the `air gap in which the vibratory member operates.

Any flux which might possibly be shunted by these externa-l members from the limbs of the local circuit containing the air gap would, oi course, be direct waste, and if there is any substantial ywaste in this way, the performf ance .of the relay, of course, would be adversely affected.; Moreover, the vibrating tongue can be pivoted most` conveniently to the limb 6 or"v the external part of the magnetie structure as by thel spring connection 9, but the use of a spring may be avoided in that the tongue can turnon a knife edge `0n that limb. It may be pointed yout', however, that the reluctance ofthe jointy between the tongue 7 and the limb 6 has to be overcome by the ,polarizing magnets 2, 3, and not by the reversals Winding 22, so that the' sensitivity of the relay does not suffer. f

The construction illustrated allows of ver synnnetrical construction illustrated therev is a biason' the armaturer 7, it indicates that there is a'steady flux flowing through the bridge-piece 20, and that thatfsteady flux is most probably due to a steady current component in the coil 22, as for example, an earth current. In order to correct this a bar magnet 27 is provided pivoted to the lower part ot the limb 6 at 28 and connectedr to ay Figure 1. This, however, is prevented byv the engagement between-the point of an adjusting screw- 31, and the side of the magnet 27 below the pivot- 28.`

` Thus, iffthe 'screw 3l is screwed back the spring 29 is allowed to draw over the magnet 27 towards the right in Figure l, whereas, if the screw 31 is .screwed forwardly7 its pointed end acts as a* cam, turning theto of the magnet 27 ktowards the left in 4igure `1. Thus, the vmagnet 27 can be turned into such a position that it assists either one or other of the permanent magnets 2, 3 vuntilfthey steady luX in the bridge-piece 2O is neutralized. e Y

The method of operation of the structure as described will be readily understood,

yrespective limb 4 or 5 and thus to enter the 4armature 7 on the opposite side.` By this reason there is a preponderance of flux entering the armature 7 on one side, the armature 7 being attracted on to that side and carrying the tongue 8 into contact with the butt 1ly or 12 on that side.

In Figure 6 asimilar motoris illustratedr which is, in effect, asynchronous motor `and can be used, for `example,as a phonic motorl for telegraphy purposes The armature 7, in this case is a bundley 'of laminations with an odd number of teeth. .'The permanent magnets V2 and `3 are of lthe shape shown, and the limb 6 is reduced here to` a vcommon pole shoe. 'The limbs 4 and 5 each have polepieces coacting with the armature 7 as before',

and the bridge-piece 20-isencircled by a coil 22, The Whole is clamped vbetween two non-magnetic plates 32, shown broken away, which' also carry the bearingsffor the spindle 33 of the'armature 7. It will be seen that on supplying an alternating current toy the coil 22, alternately a larger flux enters thefarmature 7 from the limb 4 than from they limb, 5, and vice versa. ltmay be assumed that in the position shown the tooth 34 has been attracted to thelimb 4, but in the next cycle the flux through the limb 5-preponderates and draws the tooth 35 to its pole face, and in this way continues rotating of the armature 7 is maintained, the armature rotatingk through the angle correspondingto one tooth pitch during a complete'cy'cle of the alternating current applied tothe coil 22.

fthe invention is applied to a magnetic driving unit fora loud Speaking telephone les tov

instrument, the tongue can be replaced by a reed, such as is commonly used in such instruments, which reed may be connected to drivel the diaphragm of the instrument; for example, in the case of an instrument with a large diaphragm, by a direct connection.

YWhen the invention ispapplied to a generating type ot instrument such as a magnetic electric machine, the moving member, is, of course, driven, that is to say, either oscillated or rotated, but in either case the flux in the local circuit vill be ot a fluctuating nature.

l. An electromagnetic device of the class set -forth comprising a magnetic structure consisting in the combination of a magnetic circuit of loiv reluctance containing the effective air gap of the device, a movablymounted armature included in said magnetic circuit, a coil linked with said magnetic circuit to carry lluctuating electric currents and a magnetic member co-operating with a part olf said magnetic circuit to form a circuit for a substantially steady polarizing flux with tivo paths in parallel and of substantially higher reluctance than said magnetic circuit.

2. in electromagnetic device of the class set lorth comprising a magnetic structure consisting in the combination with a pair of pole pieces with polar faces adjacent an effective air gap and a magnetic bridge piece connecting said pole pieces to form a magnetic circuit of low reluctance of a movablymounted armature located in said air gap, a

coil surrounding said bridge piece to carry iluctuating electric currents and a magnetic member co-operating with said pair of pole pieces to form a circuit 'for a substantially steady vpolarizing flux with two paths in parallel and of substantially higher reluctance than said magnetic circuit.

fr). iin electromagnetic device of the class set forth comprising a magnetic structure consisting in the combination of a magnetic cirquit of lovv reluctance containing the effective air gap of the device, a pivotallymounted armature capable of oscillating movement included in said magnetic circuit, a coil linked with said magnetic circuit to carry fluctuating electric currents and a magnetic member co-operating with a part ofl said magnetic circuit to form a circuit for a substantially steady polarizing flux with two paths in parallel and of substantially higher reluctance than said magnetic circuit.

'l-. An electromagnetic device of the class set forth comprising a magnetic structure consisting in the combination of a magnetic circuit of low reluctance containing the efiective air gap of the device, a movablymounted armature included in said magnetic circuit, a coil linked With said magnetic circuit to carry luctuating electric currents and a magnetic member co-operating with a ameno set forth comprising a magnetic structure consisting in the combination of a magnetic circuit of low reluctance containing the effective air gap of the device, a movablymounted armature included in said magnetic circuit, a coil linked with said magnetic circuit to carry fluctuating electric currents and a magnetic member embodying tivo paths in parallel for a steady polarizing flux and of substantially higher reluctance than said magnetic circuit, the magnetic circuit of the steady polarizing flux consisting of said magnetic member and a part of said magnetic circuit of low reluctance not linked with said coil.

6. An electromagnetic device of the class set forth comprising a magnetic structure consisting in the combination of a magnet-ic circuit of low reluctance containing the efl'ective air gap of the device, a movablymounted armature included in said magnetic circuit, a coil linked with said magnetic circuit to carry fluctuating electric currents and a magnetic member embodying two magnetic paths in parallel eath including a magnet producing a steady polarizing flux which tlows also through a part of said magnetic circuit of 10W reluctance not linked with said coil, said magnetic member having a. relatively hi h reluctance.

T. n an electromagnetic relay, the combination With a pair of pole-pieces with their faces adjacent the etfective air gap of the relay, a pivotally mounted armature located in said air gap and a magnetic core connecting said pole-pieces to complete a magnetic circuit of lovv reluctance, of a coil surrounding said core to carry fluctuating electric currents, and a magnetic member of higher reluctance than said magnetic circuit and embodying two magnetic paths in parallel each including a permanent magnet producing a steady polarizing linx which flows also through said pole-pieces and said armature.

8.y An electromagnetic dcice of the class set forth comprising a magnetic structure consisting inthe combination with a pair of pole pieces with polar vlaces adjacent an effective air gap and a magnetic bridge piece connecting said pole pieces to form a magnetic circuit of low reluctance with a Inovably-mounted armature located in said air gap, a coil surrounding said bridge piece to carry fluctuating electric currents, a magnetic member cti-operating with said pair oi pole pieces to form a circuit for` a substantially steady polarizing flux with two paths iio in parallel and of substantially higher reluctance than said magnetic circuit and an adjustably-mounted magnetic biassing member co-operating with said pole pieces to rbalance out the flux linked With said coil when no current is flowing.

9. In an electromagnetic relay, the combination with a pair of pole pieces having faces adjacent the effective air gap of the relay, a pivotally mounted armature located in said air gap and a magnetic core connecting said pole-pieces to compietea magnetic circuit of low reluctance, of a coil surrounding said core to carry iuctuating electric currents, a magnetic member ot higher yreluctance than said magnetic circuit and embodying two magnetic paths in p-aralel, cachincluding a permanent magnet producing a steady polarizing -flux which flows also through said pole-pieces and said armature, and an adjustably-mounted magnetic biassing member co-operating with said polepieces to balance out the flux linked With said coil when no current is ioWing.

10. j In an electro-magnetic relay, in combination, a magnetic structure formed with pole faces adjacent the e'ective air gap of the relay, a vibratory'armature located in d air gap` a coil mountedon said magnetic structure to carry fluctuating electric currents, and a biassing member adjustable during the operation of the relay, independently ot the adjustment of any other parts.

1 1. In an electro-magnetic relay, comprising in combination, a magnetic structure formed With pole faces adjacent the efl'ective air gap of the relay, a vibratory armature located in said air gap, a coil mounted on said magnetic structure to carry fluctuating electric currents., and movable magnetic member adjustable for biassing the relay during operation of the latter while the position of said abutments relatively to said tongue remains fixed.

12. In an electromagnetic relay, in combination, a magnetic structure formed With pole pieces adjacent the effective air gap of the relay, a vibratory armature mounted to cooperate With said pole pieces, a coil supported on said magnetic structure to carry fluctuating electric currents` and a magnet mounted for adjustment during the operation of the relay so as to set the bias of the relay independently of the adjustment of any other parts.

13. In an electromagnetic device of the l class set forth, the combination of a magnetic structure having a pair of opposing pole pieces with an air gap between them, a vibratory armature mounted to vibrate under thev forces of attraction of said pole piece, a coil supported on said magnetic structure to carry fluctuating electric currents and a movably mounted member for adjusting the forces of attraction of said pole pieces on said armature independently of the adjustment of other parts. n

14. In yan electromagnetic device of the class set forth, the combinationof a magnetic structure having a pair of opposing pole pieces With an air gap between them, a. vibratory armature mounted to vibrate to and from said pole piece, a coil supported on said magnetic structure to carry fluctuating electric currents andl a magnetic member movably mounted for adjustment during the operation of the device in order to set the position of said armature relatively to said pole piece independently of the adjustment of any other parts. y

In Witness whereof I hereunto subscribe. my name this 26th day of March, 1929.

RUPERT EVAN HOWARD CARPENTER. 

